I have them both because they both make money for me.Which use makes the most money? Buy the one that will help you the most.

IMO the 17TS-E is the one to buy as it is unique in its capabilities.There are a lot of low cost alternatives to the 70-200 2.8 that will get you by until you can afford one.OTOH if you are a pro just bite the bullet and buy both.

I'm in the mood for a piece of fruit. Should I have an apple or an orange?

Haha, I got a laugh out of that one!

Anyhow, Normalnorm makes a valid point that there are not cheaper alternatives to the 17TS-E (except for the rokinon that is coming out in a couple months, but that is a 24mm). But, if I were you, I would go with the 70-200mm IS ii. Between August and January, we will have the unique opportunity to photograph what is likely to be the best comet of our lifetime. Comet C/2012 S1, otherwise known as comet ISON, is the driving motivator why I picked up a 70-200 (F/4 non-IS).